Heat exchanger and especially a sodium-heated steam generator

A steam generator comprising an outer cylindrical shell having a substantial length and vertical axis and a central cylindrical and vertical body extending over the lower part of said length;

• said outer shell and said central body defining an annular space within the internal space defined by said outer shell, distributing means for supplying said annular space with liquid sodium, at least one tube bundle contained within said annular space for circulating water and in heat-exchange relation with the liquid sodium and means for maintaining a predetermined free level of sodium within said internal space and an inert gas atmosphere above said free level, each tube of the tube bundle being provided with an upper end and a lower end, the upper and lower ends of the tubes being fitted with thermal sleeves for attaching the tube ends to the outer shell and passing said ends through said shell, said ends and the entire length of said tubes between said thermal sleeves being located below said free level, said distributing means being located within said internal space above the upper ends of the tubes of said bundle and below the free level of liquid sodium, so that said at least one tube bundle and its upper ends are completely immersed within said liquid sodium, said distributing means comprising at least one nozzle, and an annular chamber located within said outer shell and above said at least one tube bundle, said chamber being fixed against said outer shell, said chamber including a horizontal bottom annular plate provided with evenly distributed holes, said annular plate extending substantially over the annular space so as to distribute evenly said liquid sodium to said annular space.